Miniature directional hydrophone



Dec. 22,1970 J, BAB|KYAN 3,550,072

MINIATURE D IRECTIONAL HYDROPHONE Filed June 26, 1969 2 Sheets-Sheet 1 FIG. 2

INVENTOR. JIRAIR A. B IKYAN I ATTORNEY 1970 J. A. BABIKYAN 3,550,072

MINIATURE DIRECTIONAL HYDROPHONE Filed June 26, 1969 2 Sheets-Sheet :1

K1 HZ INVENTUR.

JIRAIR A. BIKYAN 8Y2 ATTORNEY United States Patent 3 550 072 MINIATURE DIREcTIoNAL HYDROPHONE Jirair A. Babikyau, Providence, R.I., assignor to Sanders Associates, Inc., Nashua, N.H., a corporation of Delaware Filed June 26, 1969, Ser. No. 836,789

Int. Cl. H04r 9/04 US. Cl. 340-13 Claims ABSTRACT OF THE DISCLOSURE FIELD OF THE INVENTION This invention relates to devices in the field of acoustic detection; more particularly to hydrophones that respond mechanically to sound pressure waves thereby generating electrical signals which are representative of these waves.

THE PRIOR ART In directional hydrophones of the prior art, the electrical and mechanical parameters have largely determined the overall size of the hydrophone. More specifically, to achieve a predetermined output signal, a moveable sensing coil must cut across a magnetic field in an air gap of a magnetic circuit. Alternatively, for a given sensing coil, the value of the output signal is directly proportional to the density of the magnetic field, and the density of the field is also related to the efficient use of magnets; that is, the use of magnets which will produce the desired magnetic flux when they are operated Within their maximum energy region. Thus, when hydrophones are small they generally exhibit less magnetic and electrical efliciency and, when they are efficient, they are very large and heavy.

In addition, the size of a hydrophone bears a direct relationship with noise that is generated in the electrical signal during the operation thereof; that is, noise generated by the drag of the hydrophone as it moves through the water or as water flows around a stationary hydrophone. This noise is minimized as the overall size of the hydrophone is decreased.

A further problem in the hydrophone art is caused by a failure of electrical leads that interconnect the springcoil assembly and a terminal post of the hydrophone housing. Because the lead must move with the coil, electrical faults, such as a shorting out or a break in the lead, develop after excessive oscillatory movement thereof.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of this invention to provide a novel and improved hydrophone.

An additional object of this invention is to provide a hydrophone having a magnetic field contained therein which is equal to the field found in larger conventional hydrophones.

Another important object of this invention is to provide a hydrophone in which a spring suspending a coil also serves as a lead interconnecting the coil and terminal posts on the hydrophone housing.

It is a further object of this invention to provide a hydrophone having relatively low flow resistance and Which responds with relatively uniform noise to pressure wave signals from any direction.

According to this invention, these and other objects which will become apparent upon reading the specification are embodied in aparatus comprising a magnetic assembly which includes a permanent magnet member composed of Alnico-9 material. The magnetic member provides a magnetic field across an air gap in a magnetic circuit contained in a vented housing; and the magnetic assembly further contains a transducer means which is moveable in the air gap containing the magnetic field, which transducer means is driven by pressure waves.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded isometric of the left-hand assembly and the center section, with a section removed, of the hydrophone of this invention;

FIG. 2 is a schematic presentation of the S-spring embodiment of this invention;

FIG. 3 is an exploded sectional view of the hydrophone assembly in its assembled state taken along lines 33 of FIG. 4;

FIG. 4 is an end view of the hydrophone assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS A hydrophone apparatus embodying the invention is illustrated in FIGS. 1 and 3, and includes a substantially identical left and right hand magnetic field producing assemblies 15 and 15 which produce additive magnetic field components across an air gap space 62. A coil 44 is positioned in air gap 62 for axial movement along a central axis common to both the right and left hand assemblies. When the hydrophone assembly is submerged in water, coil 44 responds to sound pressure waves propagating through the water to move axially according to the intensity and frequency of the sound pressure waves tothereby generate an electrical signal representative of the Waves.

As mentioned previously the left and right hand assemblies are substantially identical and like components are designated by like reference numerals which are unprimed and primed for assemblies 15 and 15', respectively. Therefore, only left hand assembly 15 will be described in detail. Common to the left and right hand assemblies 15 and 15' is a ferromagnetic outer pole disc 24, a coil 44, and a ferromagnetic inner pole disc 60 collectively shown as subassembly 16.

Referring to both FIGS. 1 and 3, assembly 15 is shown to include an end bell housing 20, a permanent magnet 22, a clamping ring 26, a resilient S-spring 28, and a spacer 30. The housing 20 and magnet 22 are combined to form one subassembly, and ring 26, spring 28, and spacer 30 are connected to one side of outer pole disc 24 to form part of a second subassembly.

The cylindrical shaped permanent magnet 22 is mated with the inside of the closed surface of housing 20, and the longitudinal axis of magnet 22 is substantially aligned with the axis of housing 20. For purposes of aligning the magnet 22 within the housing 20 and to minimize losses in the magnetic field, inner surface 78 of housing 20 may be machined to assure that mating surfaces of magnet 22 and housing 20 are properly interfaced.

The ferromagnetic outer pole disc 24 interconnects housings 20 and 20, and additionally forms one edge of air gap space 62 and will be subsequently explained. Further, as previously explained, clamping ring 26, S-spring 28 and spacer 30 of the left and right hand assemblies 15 and 15 are secured to outer pole disc 24. The clamping ring 26 is positioned against side 27 of S-spring 28 with spacer 30 being positioned against the other side of spring 28. These three components (26, 28 and 30) are positioned against ridge 25 of outer pole disc 24, and

are secured thereto by any suitable means, for example, a plurality of fastening screws to form a subassembly. The clamping ring 26 and spacer 30 are preferably made from non-conducting material to electrically isolate S-spring 28 from the other components.

The S-spring 28, illustrated in FIGS. 1 and 2, is shown to have an outer element 40 and an inner element 38 suspended from the outer element by means of three curved fingers 32, 34 and 36. Preferably, one of the fingers is isolated from the other two and forms a segment of the electrical leads for coil 44. The method of isolating this finger will be explained subsequently. A coil spacing ring 42 preferably made of non-conducting material, is secured to the side of the inner element 38 towards spacer 30 by any suitable means, for example, a cement or bonding composition. Coil 44 is then cemented or otherwise secured to the opposite side of coil spacer 42.

Outer pole disc '24 contains a central bore 58 which receives a ferromagnetic inner pole disc 60 when the hydrophone is assembled. Inner pole disc 60 is mounted between the ends of magnets 22 and 22, and the disc 60 may be secured to either or both magnets by any suitable means, for example with cement. The outside diameter of disc 60 is less than the diameter of bore 58, and the distance between the edge of disc 60 and bore 58 defines annular air gap 62. Coil 44, secured to spacing ring 42, is then positioned within air gap 62 for axial movement along a central axis common to magnets 22 and 22.

A feature embodied in the present invention is to use one of the fingers of S-spring 28 as a segment of the lead which will interconnect coil 44 and a terminal post 84 (FIG. 4) on housing 20. For example, finger 34, illustrated in FIG. 2, is easily isolated from fingers 32 and 36 after subassembly 1.6 is assembled, that is, clamping ring 26, S-spring 28, spacer 30, spacing ring 42, coil 44 and the prime designates, aresecured to the outer pole disc 24. Once the components are assembled, outer element 40 of S-spring 28 is cut at points 54 and 56 and inner element 38 is cut at points 46 and 48. One end of coil 44 is then connected to the isolated section of inner ring 38 by any suitable means, such as soldering, and the isolated section of outer element 40 may be connected to terminal post 84 by a lead wire or other means well known in the art. In addition, one finger of S-spring 28' (right hand assembly) becomes a segment of the second electrical lead for coil 44. Alternatively, a lead wire may be directly connected between coil 44 and terminal post 84, but since the leads are subject to oscillatory movements they tend to fracture after extensive use causing a malfunction in the unit.

The hydrophone, illustrated in FIG. 3, comprises the left hand assembly 15, the center assembly and the right hand assembly with the sections fastened together by any suitable means, for example, bolts and nuts extend ing through a plurality of holes 64 located in the outer circumference of sections 20, and 24 as seen in FIG. 4.

FIG. 3 further illustrates appropriate design techniques to minimize the loss of magnetic flux in the hydrophone package. For example, the surface area 80 of housing 20 and the corresponding mating surface 82 of outer pole disc 24 are substantially identical, that is, the surfaces are parallel and the sharp edges are coplanar. In addition, edges leading to surface 84 of bore 58, outer pole disc 24, are beveled so that surface 84 is substantially identical in area and width to the outside surface of the inner pole disc 60. This assures that the magnetic field is concentrated within the active air gap 62, thereby enhancing the efficiency of the hydrophone.

The magnetic field that is established within the air gap 62 is the sum of the magnetic field components of the permanent magnets 22 and 22'. The path for the field components of the left hand assembly 15 extends from the permanent magnet 22 into the closed end of housing 20, radially through the fingers of housing 20 to outer pole disc 24, radially through outer pole disc 24 and across 4 air gap 62 into inner pole disc 60 and then back to magnet 20. The magnetic path for the right hand assembly extends through the corresponding prime numbered components. In addition, design procedures will provide for the use of components or cements that will minimize the loss of the resultant magnetic field.

Another feature embodied in the present invention is the use of Alnico-9 magnetic material for the permanent magnets. Since Alnico-9 magnetic material possesses very high flux density characteristics, the performance characteristics of the described hydrophone are only achieved in the hydrophones of the prior art that are four or five times in size. Conversely, the size, weight, and volume of the described hydrophone are substantially reduced. For example, the dimensions of the preferred hydrophone are approximately 2.25 inches in length, 2.20 inches in diameter at the center and weighs approximately four-fifths (0.80) of a pound.

In operation, the assembled magnetized hydrophone is immersed in a fluid which completely surrounds and fills any vacant chambers that exist in the hydrophone, the fluid entering the hydrophone structure through the vents or openings 66 and 76 in housing 20 and 20'. When a sound or vibration occurs in the monitored area, the compression waves produced by the vibrations are vented through openings 66 to 76 varying the pressure within the hydrophone, and causing coil 44 to move. Thus, coil 44 is driven back and forth through the magnetic field in air gap 62 in response to the magnitude of the sound pressure variations, and as a result of this movement through the magnetic field, a signal is generated in the coil 44. Springs 28 and 28' act in concert to restrain the movement of coil 44 due to variations of pressure, more particularly, to respond to coil motion by introducing a restoring force. The hydrophone described herein is directional, that is, the signal generated in coil 44 is a function of the cosine of the angle between the common axis of the hydrophone or the axis of the coil motion and the direction of the motion of the sound source. Thus, a resultant signal which is comprised of the signal generated in coil 44 and signals from other similar hydrophones in a unit will indicate the direction of the source. This resultant signal may be connected to any suitable electronic apparatus, for signal analysis.

The assembled hydrophone will produce a signal for analysis providing that either the left or right hand magnetic assembly is properly functioning. In particular, the signal generated by coil movement in the magnetic field produced by one assembly will be greater than one-half of the signal produced in a field generated by both assemblies, and the strength of the signal is great enough to permit detection. Thus, the hydrophone will perform its intended function providing that at least one section is producing a magnetic field.

It should be appreciated that the above-described structure may be used in apparatus other than a hydrophone placed in the ocean, for example, it may be part of a unit which is placed in the ground to detect earth vibrations.

The above description relates to specific principles of this invention, and it is to be understood that this description is made by way of example only, and not as a limitation thereon, for one skilled in the art may make modifications thereto, but still be within the true spirit and scope of thisinvention as set forth in the appended claims.

What I claim is:

1. The combination, comprising:

magnetic circuit means having an air gap and including permanent magnet means of Alinco-9 composition for providing a magnetic field within said gap; said magnetic circuit means including a first and second ferromagnetic disc, said first ferromagnetic disc having a section removed substantially in the center thereof defining an aperture and said second ferromagnetic disc being smaller than and having substantially the shape of said aperture, said first and second ferromagnetic discs being arranged to form said air gap,

vented housing means enclosing said magnetic circuit means, coil means responsive to sound pressure waves for producing electrical signals, and

suspension means positioning said coil means in said air gap.

2. The combination in accordance with claim 1, wheresaid housing means includes first and second bell shaped members each having a closed and open end and each having its open end secured to said first disc.

3. The combination in accordance with claim 2, wherein said magnet means includes two substantially cylindrical shaped members each extending from the closed end of said bell member towards said first disc, said cylindrical member being coupled to said second disc.

4. The combination in accordance with claim 1, wheresaid suspension means includes a first and second S- shaped spring assembly having an inner and outer element, said inner element being secured to said coil and said outer element being secured to said housing means.

5. A miniature permanent magnet hydrophone assembly, comprising first and second ferromagnetic housing members, each having a closed and open surface,

first and second permanent magnet members of Alinco-9 composition coupled to and extending from said closed surface to said open surface of said first and second housing members respectively, said first and second magnetic members being substantially aligned on a common axis,

a first ferromagnetic member connecting said open surface of said first housing member to said open surface of said second housing member, said first ferromagnetic member having a section removed therefrom defining an aperture,

a second ferromagnetic member connecting said first magnet member to said second magnet member, said second ferromagnetic member being positioned within said aperture,

said first and second magnet members in combination with said housings and said ferromagnetic members providing a magnetic field across the space between the wall forming said aperture and said second ferromagnetic member,

coil means responsive to sound pressure waves for producing electrical signals, said coil means being driven along the axis of said first and second magnetic members in said space, and

suspension means secured to said housing members positioning said coil means in said space, said suspension means includes a first and second S-shaped spring assembly having an inner and outer element, said inner element being secured to said coil means and said outer element being secured to said housings.

6. A miniature magnetic hydrophone assembly, comprising:

first and second bell shaped housing members, each having a closed end and an open end,

a first magnetic member extending substantially from the center of said closed end of said first housing member towards said open end, said magnetic member being substantially aligned with the center axis of said first housing member,

a second magnetic member extending substantially from the center of said closed end of said second housing member towards said open end, said magnetic memher being substantially aligned with the center axis of said second housing member,

said first and second magnetic members being comprised of Alnico-9 magnetic material,

a first spring assembly being adjacent to said first housing member,

a second spring assembly being adjacent to said second housing member,

a first ferromagnetic member being adjacent to said first and second spring assemblies, said first ferromagnetic member having a section removed therefrom defining an aperture,

means to connect said first housing member to said first spring assembly, said first spring assembly to said first ferromagnetic member, said first ferromagnetic member to said second spring assembly, and said second spring assembly to said second housing member,

a second ferromagnetic member connecting said first and second magnetic members, said first and second magnetic members being substantially on a common axis, and said second ferromagnetic member being po sitioned in said aperture,

said first and second ferromagnetic members being positioned to form a gap therebetween,

said first and second magnetic members in combination with said first and second housing members and said first and second ferromagnetic members providing a magnetic field across said gap, and

means responsive to sound pressure waves for providing an electrical signal that is a function of said waves, said means responsive being suspended between said first and second spring assemblies in said magnetic gap, and said means responsive being free to move in a plane substantially parallel to said common axis of said magnetic members.

7. A hydrophone in accordance with claim 6, wherein said first and second magnetic members are cylindrical elements.

8. A hydrophone in accordance with claim 6, wherein said first and second housings include a plurality of vent openings, said openings being arranged around the axis of said first and second magnetic members.

9. A hydrophone in accordance with claim 6 wherein said means responsive includes a coil assembly having externally accessible leads attached thereto for sensing the current in it.

10. A hydrophone in accordance with claim 9, wherein said first and second spring assemblies includes an inner and outer metallic element, said inner element being supported from said outer element by at least three metallic supporting members,

means for electrically isolating one of said supporting members from the remaining of said supporting members and said inner and outer elements, and

means connecting said isolated support member to said coil.

References Cited UNITED STATES PATENTS 2,311,079 2/ 1943 Parr, Jr. 340-13X 2,533,249 12/1950 Henson, Jr. 340-17X 2,751,573 6/1956 Millington 340-17 3,018,467 1/1962 Harris 340-17X 3,242,459 3/1966 McCollum 340-17 3,412,376 11/1968 Johnson III 340-17 RICHARD A. FARLEY, Primary Examiner B. L. RIBANDO, Assistant Examiner US. Cl. X.R. 

